1. Field of the Invention
The present invention relates to an abnormality-determining device and method for a turbo-supercharger that is provided in an internal combustion engine and has a movable member provided in an exhaust turbine thereof, for changing the area of a nozzle thereof, and an engine control unit.
2. Description of the Related Art
Conventionally, there has been proposed an abnormality-determining device of this kind in Japanese Laid-Open Patent Publication (Kokai) No. 2006-46246. This turbo-supercharger has an exhaust turbine provided in an exhaust passage of an internal combustion engine, and an intake air compressor provided in an intake passage and coaxially connected to the exhaust turbine. The exhaust turbine has a nozzle having a variable nozzle provided as a movable member. The boost pressure is controlled by actuating the variable nozzle e.g. by an actuator to vary the opening of the variable nozzle.
Further, the abnormality-determining device holds the variable nozzle at a predetermined opening degree e.g. at a fully-closed opening degree, during stoppage of the fuel supply to the engine, and determines whether or not the boost pressure detected in this state is within a predetermined pressure range. Then, if the detected boost pressure continues to be outside the predetermined pressure range for not shorter than a predetermined time period, the abnormality-determining device determines that the variable nozzle is faulty.
As described above, the conventional abnormality-determining device determines abnormality of the variable nozzle depending on whether the boost pressure detected with the variable nozzle held at the predetermined opening degree, e.g. the fully-closed opening, has turned out to be outside the predetermined pressure range. Although this makes it possible to determine abnormality of the variable nozzle when the variable nozzle is at the predetermined opening degree, e.g. at the fully-closed opening, if the variable nozzle suffers from the abnormality of the response delay, for example, the boost pressure turns out to reach the predetermined pressure range, and hence it is impossible to determine the abnormality of the response delay which the variable nozzle suffers from.